Furnace, and hot forming line including such a furnace

ABSTRACT

A furnace for heat treatment of steel sheets or steel sheet structures includes a heating zone formed by at least two furnace modules which are detachably connected to one another to thereby define a starting furnace module and an end furnace module. In order to meet increasing output requirements and capacity demands, at least one add-on furnace module is provided for placement between the starting and end furnace modules.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2006 027 625.6, filed Jun. 13, 2006, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates to a furnace for heat treatment of steel sheets or steel sheet structures, and to a hot forming line for making a hardened profiled steel sheet structure.

Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.

German Pat. No. DE 1 010 547 describes a continuous furnace for heat treatment of elongate objects such as rods or metal sheets. The furnace includes a heat channel which is made of two portions arranged exchangeably behind one another. The use of a continuous furnace in a hot forming line for making hardened profiled steel sheet structures is described in German Pat. Nos. DE 101 28 200 B4 and DE 102 54 695 B3. Continuous furnaces can be designed up to a temperature of 1,300° C., optionally also under a protective atmosphere.

Heretofore, a hot forming line is constructed to meet a certain output or production rate. This is also the base for designing the capacity of the continuous furnace within the hot forming line. As the costs for these constructions are substantial, overdimensioning of the furnace is undesired. On the other hand, the production rate of the hot forming line and furnace cannot be reliably predicted for the future, when the hot forming line is initially put into operation. It is thus conceivable that the furnace and the hot forming line reach their operational limits as a result of a change in a customer's wish or increased output demand. To address this problem, either another hot forming line needs to be built or the existing hot forming line needs to be modified. Both approaches are accompanied by significant increase in labor and costs.

It would therefore be desirable and advantageous to provide an improved furnace and hot forming line to obviate prior art shortcomings

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a furnace for heat treatment of a steel sheet or a steel sheet structure includes a heating zone formed by at least two furnace modules which are detachably connected to one another to thereby define a starting furnace module and an end furnace module, and at least one add-on furnace module which is constructed for placement between the starting and end furnace modules.

According to another aspect of the present invention, a hot forming line for making a hardened profiled steel sheet structure from a steel sheet includes a first manipulator for advancing a steel sheet, a continuous furnace receiving the steel sheet from the first manipulator for heating a steel sheet to a temperature above a microstructural transformation temperature in the austenitic state, a second manipulator receiving the heated steel sheet from the continuous furnace, a press tool receiving the heated steel sheet from the second manipulator for shaping the sheet steel into a profiled steel sheet structure, and a third manipulator removing the profiled steel sheet structure from the press tool, wherein the continuous furnace includes least two furnace modules which are detachably connected to one another to thereby define a starting furnace module and an end furnace module, and at least one add-on furnace module which is constructed for placement between the starting and end furnace modules.

The present invention resolves prior art problems by composing the heating zone of single furnace modules that are detachably connectable to one another. In effect, the furnace is designed as a modular system by which the capacity of the furnace can be easily adapted to the situation at hand and to the customer's need. A later demand for increased output can now be satisfied by simply adding one or more add-on furnace modules. As a result, the productivity or efficiency of a hot forming line, which has integrated therein such a furnace, can be enhanced, and the hot forming line can thus also be adjusted to the situation at hand. Downtimes are minimal as any modification can easily be implemented because the furnace modules can be standardized and can be constructed with their own heating units, conveyors, insulations, air supply and air discharge ducts as well detachment and coupling means.

According to another feature of the present invention, the add-on furnace module may have a length which corresponds to a total length of the starting and end furnace modules.

According to another feature of the present invention, the starting and end furnace modules and the add-on furnace module may be coupled to one another via end flanges, with a seal being disposed between end the flanges.

According to another feature of the present invention, at least one of the starting and end furnace modules and the add-on furnace module may have an inert gas supply.

As a result of the modular construction of the furnace in the form of single standardized furnace modules, which can be selectively and detachably connected with one another, the capacity and thus the productivity of a hot forming line can be adjusted to the need at hand. The throughput can be increased, using standardized components. This provides benefits as far as logistics and assembly is concerned. The furnace can be modified to increase throughput in a less time-consuming and labor intensive manner and with little costs.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a schematic illustration of a furnace according to the present invention, further depicting an add-on furnace module;

FIG. 2 is a schematic illustration of the furnace with installed add-on furnace module;

FIG. 3 is a schematic cutaway view of a coupling region between two furnace modules;

FIG. 4 is a schematic view of the coupling region, as viewed in a direction of arrow IV in FIG. 3;

FIG. 5 is a schematic illustration of a hot forming line according to the present invention, and

FIG. 6 is a schematic illustration of the hot forming line of FIG. 5 with integrated pre-forming station.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1, there is shown a schematic illustration of a furnace according to the present invention, generally designated by reference numeral 5. In its basic configuration, the furnace 5 includes an entry zone E, a heating zone H, and an exit zone A. The entry zone E essentially includes a feeding table 12 with integrated transport rolls 13. The exit zone A essentially includes a discharge table 14 with integrated transport rolls 15. The heating zone H includes two furnace modules 16, 17 which can be detachably connected to one another to thereby define a leading or starting furnace module, generally designated by reference numeral 16, and a terminal or end furnace module, generally designated by reference numeral 17.

In order to increase throughput and capacity of the furnace 5, one or more add-on modules, generally designated by reference numeral 18, can be incorporated in the heating zone H. An exemplary add-on furnace module 18 is shown in FIG. 1 and integrated in the heating zone H, as shown in FIG. 2. Installation of an add-on furnace module 18 involves initially a separation of the starting furnace module 16 from the end furnace module 17, and subsequently insertion of one or more add-on furnace modules 18 between the starting and end furnace modules 16, 17.

The furnace modules 16, 17, 18 are connected to one another via end flanges 19, 20 and screw bolts 21 via incorporation of a heat-resistant seal 22, as shown in particular in FIGS. 3 and 4. The flanges 19, 20 may, in addition, welded snugly together. On their inside, the furnace modules 16, 17, 18 are provided with an insulating lining 27 (FIG. 4)

Each of the furnace modules 16, 17, 18 is equipped with a heating unit 23 which may operate electrically or by gas. In addition, each of the furnace modules 16, 17, 18 includes a conveyor 24 for transporting steel sheets 1 through the furnace modules 16, 17, 18. Each conveyor 24 includes a chain of rollers 25. The conveyors 24 of neighboring furnace modules 16, 17, 18 extend in close proximity of one another to establish a continuous transport path.

To generate a protective atmosphere within the furnace 5, at least one of the furnace modules 16, 17, 18 is equipped with an inert gas supply 26.

The individual furnace modules 16, 17, 18 have standard dimensions, with the add-on furnace module 18 having a length L₁₈ which is suitably twice a length L₁₆ of the starting furnace module 16 or twice a length L₁₇ of the end furnace module 17. For example, the furnace module 16 and the end furnace module 17 may jointly have an overall length of 6 m so that the furnace 5 may be assembled of 6 m units. As a result, the length L₁₈ of the add-on furnace module 18 is about equal to the joint total length of the starting and end furnace modules 16, 17.

Referring now to FIG. 5, there is shown is a schematic illustration of a hot forming line according to the present invention which is provided for making a hardened profiled steel sheet structure from a steel sheet 1 and has incorporated a furnace 5. Hardened profiled steel sheet structures find application in the automobile industry, for example as A pillars, B pillars, or C pillars, as door impact carriers, or bumpers. Sidewall structures of a motor vehicle body are also produced nowadays, using a hot forming process and hardening in a press tool.

In the hot forming line, the steel sheet 1 is initially reeled off a coil 2 and straightened and then cut to size in a punching or cutting device 3. Optionally, the steel sheet 1 may be pre-formed, before being transferred by a first manipulator 4 to the furnace 5, constructed in the form of a continuous furnace. Pre-forming of the sheet steel 1 is realized by a press 6 which is positioned upstream of the furnace 5 and in which the steel sheet 1 is shaped and, optionally trimmed, as shown in FIG. 6. The provision of the press 6 is the only difference between the hot forming lines of FIGS. 5 and 6.

The furnace 5 heats the steel sheet 1 to a temperature above the microstructural transformation temperature in the austenitic state. Depending on the steel grade, this temperature ranges between 700° C. and 1,100° C. Suitably, the atmosphere of the furnace 5 is rendered inert by a targeted and sufficient supply of protective gas so as to prevent scaling of the steel sheet surface. A second manipulator 7 accepts the heated steel sheet 1 and transfers it into a press tool 8, where the steel sheet 1 is shaped into the final profiled steel sheet structure 9 and rapidly cooled down with the aid of a cooling unit 10, thereby establishing a fine-grained martensitic or bainitic material microstructure. The profiled steel sheet structure 9 is hereby hardened with a precisely tailored material strength. A third manipulator 11 is arranged downstream of the press tool 8 to remove the shaped and hardened profiled steel sheet structure 9 from the press tool 8 and to transfer it to an unillustrated container.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A furnace for heat treatment of a steel sheet or a steel sheet structure, comprising a heating zone formed by at least two furnace modules which are detachably connected to one another to thereby define a starting furnace module and an end furnace module, and at least one add-on furnace module which is constructed for placement between the starting and end furnace modules.
 2. The furnace of claim 1, wherein the add-on furnace module has a length which corresponds to a total length of the starting and end furnace modules.
 3. The furnace of claim 1, wherein the starting and end furnace modules and the add-on furnace module are respectively coupled to one another via end flanges, with a seal being disposed between the end flanges.
 4. The furnace of claim 1, wherein the starting and end furnace modules and the add-on furnace module are each constructed with a heating unit.
 5. The furnace of claim 1, wherein the starting and end furnace modules and the add-on furnace module are each constructed with a conveyor.
 6. The furnace of claim 5, wherein the conveyors of the starting and end furnace modules and the add-on furnace module are constructed for linkage to one another.
 7. The furnace of claim 1, wherein at least one of the starting and end furnace modules and the add-on furnace module has an inert gas supply.
 8. A hot forming line for making a hardened profiled steel sheet structure from a steel sheet, comprising: a first manipulator for advancing a steel sheet; a continuous furnace, receiving the steel sheet from the first manipulator, for heating the steel sheet to a temperature above a microstructural transformation temperature in the austenitic state; a second manipulator receiving the heated steel sheet from the continuous furnace; a press tool, receiving the heated steel sheet from the second manipulator, for shaping the sheet steel into a profiled steel sheet structure; a third manipulator removing the profiled steel sheet structure from the press tool, wherein the continuous furnace includes least two furnace modules which are detachably connected to one another to thereby define a starting furnace module and an end furnace module, and at least one add-on furnace module which is constructed for placement between the starting and end furnace modules.
 9. The hot forming line of claim 8, further comprising a press, disposed upstream of the continuous furnace, for pre-forming the steel sheet.
 10. The hot forming line of claim 8, wherein the add-on furnace module has a length which corresponds to a total length of the starting and end furnace modules.
 11. The hot forming line of claim 8, wherein the starting and end furnace modules and the add-on furnace module are respectively coupled to one another via end flanges, with a seal being disposed between the end flanges.
 12. The hot forming line of claim 8, wherein the starting and end furnace modules and the add-on furnace module are each constructed with a heating unit.
 13. The hot forming line of claim 8, wherein the starting and end furnace modules and the add-on furnace module are each constructed with a conveyor for longitudinal transport of the steel sheet through the starting and end furnace modules and the add-on furnace module.
 14. The hot forming line of claim 13, wherein the conveyors of neighboring ones of the starting and end furnace modules and the add-on furnace module are constructed for linkage to one another.
 15. The hot forming line of claim 8, wherein at least one of the starting and end furnace modules and the add-on furnace module has an inert gas supply.
 16. A modular furnace assembly, comprising: a plurality of first furnace modules detachable connectable to one another to establish a heating zone; and one or more add-on second furnace modules for incorporation between two of the first furnace modules for increasing a length of the heating zone.
 17. The furnace assembly of claim 16, wherein the add-on furnace module has a length which corresponds to a total length of two first furnace modules. 